1. Field of the Invention
This invention relates to computer systems and, more particularly, to the organization of registers in the central processing unit of a computer system.
2. History of the Prior Art
In the digital computers of the prior art, registers make up the primary means of accomplishing the mathematical and logical operations. For example, in an add operation, a first number is stored in one register, a second number is stored in a second register, and the numbers in each are combined and stored in a third register. Each register is essentially an area capable of storing a convenient number of digits (usually in binary form) to represent the data and instructions with which the computer system deals. In some systems these registers are physical portions of hardware specific to a particular use as a register; in others, the registers are parts of general memory mapped in such a way that they may be utilized as registers. In some cases these registers have specific functions; in others, they may be used for any of a number of functions.
In computer systems, it has been determined that greater system speed can be attained, in general, with a larger number of registers because, among other things, with a larger number of registers a number of operations may be running concurrently before the necessity of storing intermediate results in general memory is reached. Consequently, some modern computer designs involve central processing units (CPUs) with as many as one hundred and twenty-eight individual registers.
Obviously, as the number of registers available to a processor grows, the complexity of the circuitry for addressing a register, and for loading and emptying its contents, also grows. Ultimately, this increase in the number of registers becomes counter-productive; and the overhead imposed on the system becomes greater than the additional speed provided by the additional registers.
Various means of overcoming this limitation have been tried. In general, these means have involved using higher speed components for the registers and attendant circuitry. However, in advanced systems making use of processors which are conventionally organized, this effort is to no end because the real limiting factor at the operating speeds attained is the speed of electricity.